A tube cutoff apparatus is typically employed at the end of a tube fabricating mill to cut the tubing into lengths as it emerges from the mill. Cutoff apparatus is also used for recut operations where it is desired to cut an existing piece of finished tubing into several shorter lengths.
A known tube cutoff apparatus comprises a press and a die set operated by the press. The die set is adapted to accommodate a particular shape and size of tubing and includes means for holding one or more blades which are used in the cutoff operation. A so-called "single-cut" apparatus employs a single blade which is driven by the press and die set through the tubing. A single cut apparatus typically leaves a dented or distorted end on the tubing and, therefore, may require secondary operations to restore the tube end to a round configuration. A so-called "double cut" apparatus comprises a first blade which passes across a section of tube wall to scarf or notch the tubing, and a second blade which is thereafter driven through the tubing using the notch as an entry point. Given blades of proper construction and condition, this apparatus tends to produce an undistorted or "dimple free" tube end.
There are several approaches which may be taken to the design of a double cut apparatus. One approach is illustrated in U.S. Pat. No. 4,109,555, issued Aug. 29, 1978, to Alexander Borzym and assigned to Alpha Industries, Inc. of Novi, Mich. In this device, the notching blade is driven by a cam depending from an upper die set platen through a cutting stroke and a return stroke immediately prior to the entry of a second severing blade. Another approach is illustrated in U.S. Pat. No. 4,108,029, issued Aug. 22, 1978, to Alexander Borzym and assigned to Alpha Industries, Inc. In this device, the notching blade is also driven by a depending cam, but is drawn across the tubing in a single unidirectional stroke as the upper platen descends and is returned to a home position as the die set is reopened. This single stroke or "draw across" approach is also illustrated in U.S. Pat. No. 4,294,147, issued Oct. 13, 1981, to John J. Borzym.
An advantage of the latter design approach; i.e., the single stroke or "draw across" design, is that the notching blade moves in a single direction as the die set is closed and tends to permit the double cut operation to be achieved in a shorter vertical stroke and with less strain on moving parts. The notching blade is returned to a home position as the die set is reopened. It will be understood by those skilled in the art that although the cutoff apparatus may be employed or used in a variety of orientations, the notching blade is typically referred to as the "horizontal blade" and the severing blade is typically referred to as the "vertical blade" and these terms are adopted in this specification without special regard to actual direction.